<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        .aa::after {
            content: "123";
            color: #f00;
        }

        .aa:before {
            content: "567";
            color: skyblue;
            font-size: 33px;
        }

        .bb::first-letter {
            color: #0000ff;
            font-size: 22px;
        }
        input:focus{
            color: #ff0;
        }
        input:link{
            color: #0000ff;
        }
        input:visited{
            color: black;
        }
        input:hover{
        font-size: 33px;
        }
        input:active{
            font-size: 44px;
        }
    </style>
</head>

<body>
    <h1>weilei</h1>
    <p class="aa">伪类</p>
    <p class="bb">123</p>
    <input type="text" value="123">
</body>

</html>